This invention relates to the transmission of rotational mechanical power by means of a torque exchange coupling.
Of the several types of devices employed for merely transferring rotational mechanical power (as distinguished from devices that modify torque), those used most frequently are dependent upon either friction, e.g., friction clutches and friction brakes, or upon hydraulic action, e.g., fluid couplings. Each of these familiar types of devices has disadvantages. A friction clutch, during the process of coming into engagement, and a friction brake, while it is applied and slipping, generate heat. This heat represents wasted energy and is associated with undue wear and with a corresponding need for frequent repair and replacement. When the amount of heat becomes very great, it may impair the structure of the mechanism. In addition to producing heat in undue amounts, frictional braking devices in the prior art have other faults, viz., fading (when affected by heat or foreign matter on the contact surfaces) and locking. The functioning of frictional devices in the prior art is impaired also when by accident moisture, lubricant, or other foreign matter is present on the surface where friction is designed to operate. A hydraulic coupling generates heat at all times during operation under load, owing to the fact that it does not attain a locked relationship between the rotating parts; rather, the liquid element is constantly sheared by the blades, entailing wasted energy as well as production of heat. Hence, a hydraulic coupling ordinarily requires provision for cooling.
The above-mentioned familiar devices have the further limitation that they operate efficiently and have a reasonable span of useful life only when their component parts are closely aligned.
A friction clutch has additional drawbacks when it is used in transmitting power produced by an internal combustion engine. The drawbacks arise both from the characteristics of the engine and from the characteristics of the clutch. The peculiarities of the engine are (1) that at low velocities it generates only a small part of its rated power, and (2) that it can be adjusted for high efficiency in operation only over a narrow part of its total range of velocities. A friction clutch engages with comparative abruptness. It follows that, when a friction clutch is used in connection with an internal combustion engine, provision must be made (1) to keep the load from straining or stalling the engine at the time of first engagement or whenever the load is severe and the speed slight, and (2) to keep the combined mechanism from being racked by abrupt starting engagement. In motor vehicles, adjustment is made for these difficulties, commonly, either (1) by tuning the engine in such a manner as to heighten its efficiency at very low speeds, whereby its tuning becomes inefficient for high speeds, (2) by providing a considerable variety of gear ratios,--typically three or four forward speeds--, or (3) by employing a combination of gear sets and a torque converter.